Automatic draft regulator for furnaces



Feb. 9 1926. r 1,572,277

| P. FESSENDEN E1 AL 7 AUTOMATIC DRAFT REGULATOR FOR FURNACES Filed August 8, 1921 iii 1mph z A /-fl mull-lulu zfz lmnzarzimra W 0 v 4255672 21/ 6. w. If? F ZAHorney-z:

Patented Feb. 9, 1926.

UNITED STATES i,572,277. PATENT OFFICE.

LOUIS I. FESSENDEN AND HARRY R. ELLIS, OF SHEBOYGAN, WISCONSIN, ASSIGNOBS TO THE FESSENDEN-ELLIS COMPANY,

TION or WISCONSIN.

0F SHEBOYGAN, WISCONSIN, A CORPORA- AUTOMATIC DRAFT REGULATOR FOR FURNACES.

Application filed August 8, 1921.

To all whom it may concern:

Be it known that we, LOUIS P. FEssEN- DEN and HARRY R. ELLIS, citizens of the United States, residing at Sheboygan, in the county of Sheboygan and State of Visconsin, have invented new and useful 1mprovements in Automatic Draft Regulators for Furnaces, of which the following is a specification.

This regulator is designed to regulate the pressure over the fire in the combustion space of a forced draft stoker installation as generally applied to steam boilers, where the air for the combustion of the fuel is furnished under pressure to the under side of the fuel bed and the products of combustion are carried away from the draft or suction furnished usually by a chimney or stack, although this function issometimes taken care of by what is known as an induced-draft fan. In this description we will assume the draft is furnished by a stack although the regulator is equally applicable to the control of an induced-draft fan. In an installation like that described, the undergrate supply of air is regulated usually by varying the speed of the blower by a regulator which responds to variations in the steam header pressure, and there are many different makes of such regulators, that give very satisfactory results.

From an economical standpoint both as to quantity of fuel consumed and the maintenance of the furnaces and boilers, the proper draft to be carried over the fire has been found to be just enough below atmospheric pressure as to carry the products of combustion up the stack, rather than to force them out into the fireroom.

To maintain such a slight draft, with a fuel bed ever tending to change its thickness, due to various sizes and quality of fuel and an undergrate pressure varying with the changes in demand for steam, requires a regulator of great sensitiveness. Many attempts have been made to regulate this over-fire draft by regulators functioning from the header pressure, but as no relation exists between the two they have not proven successful, so that in most cases, the uptake damper is set in such a position that at full blower pressure, there will be draft enough maintained by the stack to carry away the products of combustion Serial No. 490,631.

without putting pressure above atmosphere in the combustion space, and with the inevitable result that at all other blower pressures there is too much draft accompanied by loss in economy of fuel and maintenance of furnaces due to infiltration of air.

In order that the invention may be better understood, reference is had to the accompanying drawing, forming a part of this specification, in which;

Figure 1 is an elevation of the apparatus partly in section, and Fig. 2 is an enlarged elevation of a compensating device.

As the pressure to be regulated is the pressure in the combustion space 18 of a furnace, that pressure is made use of to move a freely suspended inverted cap or cylinder 2 open on its lower end, in a container 1 which is partly filled with oil, water or any other liquid to form a seal between the pressure which exists under the ,cylindcr 2 through connecting pipe 3 which goes to that part of furnace combustion space 18 wherein the pressure is to be regulated. Container 1 has a cored passage 22 from a point where connecting pipe 3 is attached which conveys the pressure existing in the-furnace combustion space 18 to the area above the water seal in cylinder 1. The top side of cylinder head is acted upon by the atmospheric pressure of the surrounding air. Cylinder 2 is connected by a flexible or other connection 4 to a balance beam 5 which is fulcrumed on a bracket 6 by a knife edge 23 and carries a weight pan 8 which latter, as well as the connection 4 are also suspended on knife edges so as to make the balance beam 5 practically frictionless. Balance beam 5 also carries a slidable poise 7 to assist in the finer adjustment of balance. 0perating cylinder 11 and pilot "alve 10 are wellknown commercial devices used in connec tion with various automatic mechanisms and their action is so well understood that it is not necessary to describe the same in detail except as it may be necessary to refer to their action I in connection with the present apparatus. The pilotvalve 10 is connected to balance beam 5 through a ball-and-socket connection 9 inserted in. valve stem of the pilot valve 10 to render its action as frictionless as possible due to any misalignment and also because the motion derived and at rest.

' 8116d amount of compensation can 17 when a flexible connection is used to con-' nect the regulator and the lever 14. l The operation of the apparatus is as folows:

Connection 13 is adjusted so that upon maximum travel of plunger 12 of operating cylinder 11, the damper 15 will travel from full en to full shut osition or whatever part 0 that travel may I deemed necessary. The weighton balance beam are so adjusted that when pressure in combustion space 18 is that which it is desired to maintain, balance beam 5 will be in horizontal osition In this position cy inder 2 should be in mid-position of its travel in container 1 and valve stem 9 should be so adjusted that there .will be no movement of plunger 12. This condition of rest will continue as long as the ressure in combustion s ace 18 does not ten to change. But a very 'ght change in this combustion space pres-- sure will cause cylinder 2 to move up or down, down for a decrease in pressure and up for an increase, thereby movin balance arm 5 correspondingly, and throng it causing ilot valve to admit fluid to one side or the other of plunger 12 in cylinder 11, which in turn moves damper 15 to a posi tion where all parts will again be at rest with the pressure in combustion space 18 at its predetermined value.

In practice it was found that, uue to a small time interval between the time the damper moves and the reestablishment of the predetermined ressure in combustion space, a huntin action of regulator wouldbe set up, and w ile the predetermined ressure would be held very close, the regu ator would be ke t in motion continuously. This hunting action is taken care of by a compensatin device, which is very simple, but a valuab e part of the invention. It consists of two springs which may be applied to balance beam 5 either side of fulcrum point 23 so that when balance beam 5 isat rest,

in its neutral position,'which is horizontal, no pressure is exerted by springs on the beam. Any movement of beam 5 in either direction however is resisted by a constantly increasing tplressure of the spring which opposes it in e direction it tends to move. By adjusting tension in these spring:a any deattained and the aforementioned lag or time element in change of furnace pressure is overcome and hunting action of the regulator obviated. The drawing shows these springs 19 as flatsprings mounted on suitable support, their free ends, bearing on balance beam 5.

The counter balance system com rising the beam 5with its counter weights and 8 on one side of the fulcrum 23 and the weight of the cup or piston 2 on the other side of the fulcrum has a natural period of vibration, which is not secured by the balancing springs 19, since the are resilient and do not dissipate ener the system. The %amping out of the periodic or natural vibration of the system is performed b the bell or cup 2 and its liquid seal in the c amber 1, which thus performs the dual function of a piston and also of a dash pot. a

The prevention of huntin of the regulator is a different problem. e springs 19 secure the function of preventing huntin by providing a resistance increasin wit deflection o crating in con'unction with the valve 9, which admits flui morerapidly to the working 0 linder for increased deflection of the beam. bus the response is graduated to conform to the intensity of the disturbance and hence overthrow with consequent huntin does not occur.

\Ve 0 not confine ourselves to this particular construction as many modifications c i the application of a s ring or springs to do thersame thing might evolved.

'As the position of plunger 12 and damper 15 is an indication of the volume of gases passing through boiler gas passages and thus 0 the demand on boiler for steam, advantage is taken of this relation to control the speed of stoker engines and thereby the quantity of and time of feeding fuel to furnace. This is accomplished by connect ing stoker control valve 21 b a flexible connection to plunger 12 an adusting it so that with plunger at extreme top of its travel in cylinder 11, the s ed of stoker engine will feed just 'enou fuel to keep fuel bed at a proper thic ess, and that when plunger 12 is at' other end of its travel stoker s d will be such as to maintain the fuel be at its proper thickness under these conditions of draft. It follows that any intermediate points of travel of plunger 12 will give a proportionate stoker 5 ed to maintain the fuel bed at a proper thickness. On the drawing is shown the control valve of a well known stoker of the underfeed ram ty The result would be the samevif connection were made to a chronometer valve controlling speed of engine-driven stokers.

We claim:

In a regulator of the-class described, an

ut merely return it to ing c linder for operating a furnace control mein er, a pilot valve for said 0 erating cylinder, said valve being reversi le and having a neutral osition, said beam being normally balanced when a predetermined gas pressure acts upon said cup piston, said pilot valve being connected to said beam and bein in neutral position when the beam is norma ly balanced, and spring means for said beam to afford increasing resistance for 10 increasing deflection of the beam either way from normally balanced position, said liquid sealed cup piston serving as a dashpot to steady the weighted beam against vibration.

In testimony whereof we ailix our signa- 1 tures.

LOUIS P. FESSENDEN. HARRY R. ELLIS. 

